Moraxella catarrhalis, also known as Moraxella (Branhamella) catarrhalis or Branhamella catarrhalis and formerly known as Neisseria catarrhalis or Micrococcus catarrhalis, is a gram-negative bacterium frequently found in the respiratory tract of humans. M. catarrhalis, originally thought to be a harmless commensal organism, is now recognized as an important pathogen in upper and lower respiratory tract infections in humans. In humans, M. catarrhalis causes serious lower respiratory tract infections in adults with chronic lung disease, systemic infections in immunocompromised patients, and otitis media and sinusitis in infants and children (Helminen et al., 1993, Infect. Immun. 61:2003–2010; Catlin, B. W., 1990, Clin. Microbiol. Rev. 3:293–320; and references cited therein). The outer surface components of Moraxella catarrhalis have been studied in attempts to understand the pathogenic process of M. catarrhalis infections and to develop useful therapeutic treatments and prophylactic measures against such infections. The outer membrane proteins (OMPs) in particular have received considerable attention as possible virulence factors and as potential vaccine antigens. M. catarrhalis has over 20 different OMPs with 6 to 8 of these, OMPs A to H, as the predominate species (Murphy and Loeb, 1989, Microbial Pathogen. 6:159–174). The molecular weights of OMPs A to H range from 98 to 21 kD, respectively (Bartos and Murphy, 1988, J. Infect. Dis. 158:761–765; Helminen et al., 1993, Infect. Immun. 61:2003–2010; Murphy et al, 1993, Molecul. Microbiol. 10:87–97; and Sarwar et al, 1992, Infect. Immun. 60:804–809). Comparisons of protein profiles by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) of outer membrane preparations from 50 M. catarrhalis strains show nearly homogeneous patterns of OMPs A to H (Bartos and Murphy, 1988, J. Infect. Dis. 158:761–765).
In intact bacterium or bacterially-derived outer membrane vesicles, several of the above-identified OMPs present surface-exposed epitopes that elicit the production of antibodies that bind the OMPs. These antigenic OMPs include OMP E and OMP G (Murphy and Bartos, 1989, Infect. Immun. 57:2938–2941); OMP C/D (Sarwar et al., 1992, Infect. Immun. 60:804–809); CopB, an 80 kD OMP, (Helminen et al., 1993, Infect. Immun. 61:2003–2010); and UspA (Helminen et al., 1994, J. Infect. Dis. 170:867–872).
The therapeutic potential of antibodies to surface-exposed epitopes of outer-membrane proteins of M. catarrhalis is generally examined by the cytotoxic (bactericidal) activity, because there is no animal model of disease. The only natural host for disease caused by Moraxella is human. However, others have studied the role of antibodies in an animal model of Moraxella lung clearance. The model involved direct bolus inoculation of lungs of BALB/c VAF/Plus mice with a controlled number of M. catarrhalis cells and subsequent examination of the rate of pulmonary clearance of the bacteria (Unhanand et al., 1992, J. Infect. Dis. 165:644–650). Different clinical isolates of the M. catarrhalis exhibited different rates of clearance, all of which are relatively rapid, that correlated with the level of granulocyte recruitment into the infection site. Passive immunization with a monoclonal antibody directed to a surface-exposed epitope of CopB and UspA increased the rate of pulmonary clearance of M. catarrhalis (Helminen et al., 1993, Infect. Immun. 61:2003–2010; Helminen et al., 1994, J. Infect. Dis. 170:867–872). There remains a need for compositions and methods for diagnosis of, as well as, prophylactic and therapeutic treatments for infections caused by M. catarrhalis. 
The adherence of bacterial pathogens to a host cell surface promotes colonization and initiates pathogenesis. See, E. H. Beachey, 1981, J. Infect. Dis. 143:325–345. Gram-negative bacteria typically express surface lectins that bind to specific oligosaccharides of glycoproteins and/or glycolipids on the host cell surface. Such lectins are often associated with pili or fimbriae. Bacterial adherence can also occur by non-specific binding resulting from hydrophobic and/or charge interaction with the host cell surface.
The mechanism of M. catarrhalis adherence to cells of the respiratory tract remains poorly understood. The organism adheres to cultured human nasopharyngeal epithelial cells. Another study suggests that fimbriae may have a role in the adherence to such cells as fimbriae denaturation or treatment with anti-fimbriae antibodies reduced adherence by fimbriated strains. Fimbriae mediated binding, however, cannot be the sole basis of this adherence as the most highly adhering strain, among the several examined, was a non-fimbriated strain. Thus, other unidentified components are involved in the bacteria's adherence.